This invention relates generally to automotive disc brake assemblies, and more particularly, to a method and apparatus for mounting a disc brake rotor on a bearing hub during handling, shipping and installation of a wheel on the disc brake assembly.
Virtually all modern passenger automobiles and most modern trucks employ disc brake systems on at least the front wheels of those vehicles. When the driver depresses the brake pedal, a hydraulic system forces brake pads against each side of a disc-shaped, metallic brake rotor. This rotor is attached the automobile at a bearing hub, which is connected to the suspension system. The respective axes around which the bearing hub and the disc brake rotor rotate must be precisely perpendicular to their respective mating surfaces and also aligned with each other to maximize the efficiency and life of the braking system. Misalignment between the rotor and bearing can be caused by any combination of a number of factors including imperfections in the hub and rotor mounting surfaces, inaccuracy in the geometry of the respective parts, improper surface finishing of the rotor or the hub and contaminates or debris.
Brake technicians typically measure misalignment between the bearing hub and the disc rotor using special tools. These tools measure the maximum deflection in the rotor surface which is known as xe2x80x9crunoutxe2x80x9d. Typical manufacturer specifications establish a standard acceptable runout as no more than approximately 0.002-0.003 inches. Commonly, the rotor is indexed or rotated until it is optimally mated on the bearing hub to achieve the best possible assembled lateral runout relationship.
During the assembly and manufacturing process of an automobile, the disc brake assembly is typically manufactured and assembled at one location and then transported to another location for assembly with the vehicle wheel and the remainder of the vehicle. As such, the optimal mated relationship between the disc rotor and the bearing hub must be maintained during handling and shipping of the disc brake assembly.
Currently, two methods are typically used to keep the rotor retained to the bearing in such situations. The first method uses a small set screw which threads through a hole in the disc rotor and into a corresponding hole in the bearing to keep the rotor in place on the bearing. However, multiple holes are commonly drilled into the rotor to align the set screw with a predrilled hole in the bearing. Only one of the multiple holes is typically used depending upon the desired orientation of the disc relative to the bearing for optimal runout. Therefore, the non-used or extra holes in the rotor increase the chance of dust, rust and other contaminates collecting in those holes. The non-used or extra holes also present problems and make it difficult to balance the rotor.
The other method commonly practiced today to retain the rotor to the bearing uses Tinnerman nuts or push nuts to keep the rotor in place. The push nuts are press-fit over studs projecting from the bearing after the rotor is seated on the bearing. Typically, at least two, and commonly more, push nuts are used to keep the rotor in place on the bearing by the interference fit between the stud and the push nut. However, pockets or recesses in the rotor or wheel are typically used to accommodate and provide clearance for the push nut. The pockets or recesses are formed in the rotor or wheel surrounding the holes which receive the studs from the bearing. The pockets or recesses remove valuable material from the rotor or wheel around the studs thus decreasing the stiffness in that area of the disc brake assembly and, likewise, increasing the potential runout of the disc brake system. Moreover, the push nuts must be in a specific orientation to work properly thus requiring a conscious effort and an attention to detail for the technician when mounting the push nut.
Therefore, because of the problems associated with existing systems and methods for mounting a disc rotor to a bearing hub, a need continues to exist for an efficient, inexpensive and effective method for doing so without detrimentally impacting manufacturing costs, efficiency and resulting lateral runout of the disc brake assembly.
This invention efficiently, effectively and inexpensively solves the above-mentioned problems and other problems of known methods and systems for mounting a disc brake rotor to a bearing hub without detrimentally impacting the lateral runout of the disc brake assembly. A presently preferred embodiment of this invention provides a simple and effective device to keep the brake rotor and bearing together during handling, shipping and the installation of the vehicle wheel. In one form, the invention includes a retaining clip which is inserted or snapped into a groove which is machined or otherwise formed in the outer circumference of the pilot hub projecting from the bearing after the disc brake rotor is assembled to the bearing. The clip in a present form is a generally circular split-ring which has a smaller inner diameter than the diameter of the groove in the pilot hub bearing. After the runout between the disc rotor and the bearing hub is gauged and minimized, the split-ring clip is expanded and inserted into the groove on the pilot hub bearing. The expansion and resulting preload on the clip ensures a tight fit. The clip acts as a physical block or detent keeping the rotor positioned against the bearing flange in the desired orientation. The groove in the bearing is machined entirely around the pilot hub, thus eliminating the need to orient the clip onto the bearing unlike prior methods and systems for retaining the rotor on the bearing hub.
In an alternative embodiment of this invention, the groove in the pilot hub includes a beveled edge that allows for the clip to fit snugly against the pilot hub and the rotor with both maximum and minimum material tolerance conditions. The depth of the groove in the pilot hub must be adequate to ensure that the size of the clip does not interfere with the diameter of the brake rotor at a minimum material condition. In a further alternative embodiment, a step is machined in the brake rotor adjacent to the hole through which the pilot hub projects to allow for the use of common bearing applications with different rotor designs. Moreover, the step provides additional clearance for non-standard wheel designs. The clip is designed to be small enough so as not to interfere with the wheel during operation of the vehicle. Moreover, the clip retains the rotor flush on the bearing and does not allow contaminants between the rotor and bearing which can contribute to lateral runout. Furthermore, the clip keeps the bearing and rotor mated together after they have been indexed and gauged for runout.
The orientation of the clip in the groove is not a consideration so the assembly of the clip to the bearing is much less difficult than the implementation of prior systems and methods thereby improving the manufacturability of the disc brake assembly. As such, the assembly process is much less complex and orientation of the screws, push nuts or the like is not a concern with this invention. The clip keeps the rotor in place during manufacturing and shipping and is not removed after the wheel is installed. The clip is small enough so as not to interfere with the wheel when it is assembled so the clip does not need to be removed from the groove. Moreover, lateral runout is improved due to the fact that pockets or recesses are not required in the rotor or the wheel to accommodate the push nut or Tinnerman nut utilized in prior systems and methods.
As a result of this invention, an improved, more efficient and inexpensive system and method is provided for mounting and retaining a disc brake rotor on a bearing hub during initial assembly, installation and shipping compared to known prior art designs.